Capillary zone electrophoresis separation parameters

Subsequently four different CE modes are described in the sections Capillary Zone Electrophoresis, Capillary Gel Electrophoresis, Capillary Isoelectric Focussing, and Micellar Electrokinetic Chromatography (MEKC), respectively. The fundamental principles of the specific separation modes are briefly explained, using appropriate equations where required. In Table 3 all equations are listed. In addition, the influence of both instrumental parameters and electrolytic solution parameters on the optimization of separations is described. 

Rathore, A. S., and Horvath, C. S. (1996). Separation parameters via virtual migration distances in high-performance liquid chromatography, capillary zone electrophoresis and electrokinetic chromatography /. Chromatogr. A 743, 231-246. 

Berzas Nevado et al. [138] developed a new capillary zone electrophoresis method for the separation of omeprazole enantiomers. Methyl-/ -cyclodextrin was chosen as the chiral selector, and several parameters, such as cyclodextrin structure and concentration, buffer concentration, pH, and capillary temperature were investigated to optimize separation and run times. Analysis time, shorter than 8 min was found using a background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.2, 30 mM /1-cyclodextrin and 5 mM sodium disulfide, hydrodynamic injection, and 15 kV separation voltage. Detection limits were evaluated on the basis of baseline noise and were established 0.31 mg/1 for the omeprazole enantiomers. The method was applied to pharmaceutical preparations with recoveries between 84% and 104% of the labeled contents. 

The fundamental separation mechanism of capillary zone electrophoresis (CZE) is based on differences in the mobilities of solutes. Mobility is defined as the charge/mass ratio for each solute. Since the charge is often a function of pH, the pH is the most important adjustable parameter for control of resolution. The order of elution on bare silica at high pH is cations, unseparated neutrals, and anions. At low pH, where the EOF is very low, the anions may migrate toward the positive electrode and may not be seen using normal polarity. 

Issaq, H.J. Atamna, I.Z. Muschik, G.M. Janini, G.M. The effect of electric field strength, buffer t)fpe and concentration on separation parameters in capillary zone electrophoresis. Chromatographia 1991, 32, 155-161. 

Lukacs, K. D. and J. W. Jorgenson, Capillary zone electrophoresis Effect of physical parameters on separation efficiency and quantitation, J. High Res-olut. Chromatogr. Chromatogr. Commun. 8 405-411 (1985). 

Capella-Peiro et al. (28) used a 3 full factorial design to optimize the capillary zone electrophoresis (CZE) separation of a group of seven antihistamines (brompheniramine, chlorpheniramine, cyproheptadine, diphenhydramine, doxylamine, hydroxyzine, and loratadine). In this case, critical parameters such as pH (a concentration of 20 mM phosphate was kept constant in all the experiments) and the applied voltage were studied to evaluate their effect on the resolution and efficiency. Maximum response was achieved at pH 2.0 and an applied voltage of 5 kV. After a repeatability study to check the precision of the electrophoretic method, as well as a suitable calibration, the usefulness of this optimized method was demonstrated through the determination of the listed histamines in pharmaceuticals, urine, and serum samples (recoveries were in agreement with the stated contents). Urine samples were diluted and directly injected in the CE system, while serum samples were previously extracted by means of a solid-phase extraction (SPE) procedure. 

Capillary electrochromatography is a hybrid separation method that couples CE with HPLC. It combines the high separation efficiency that capillary zone electrophoresis (CZE) offers with the wide range of parameters that can be manipulated in HPLC, particularly the wide range of stationary phases from which to choose. Subsequently, CEC has become a powerful technique that has gained... 

Capillary zone electrophoresis, CZE, is the simplest CE mode in which the separation is based on differences in the charge-to-mass ratio of the analytes. This approach can be effective in a number of applications in particular, quaternary alkaloids owing to the permanent charge are ideal solutes in CZE, regardless of the pH of the running buffer. Below, the most important parameters affecting the CZE separation will be considered with emphasis on the relevant aspects involved in analysis of alkaloids in herbal drugs and medicinal plants. 

Vincristine (VC) and vinblastine (VB) are dimeric catharanthus alkaloids isolated from the plant Catharanthus roseus. A capillary zone electrophoresis (CZE) was conducted for systematic and comprehensive study of the separation and quantification of two dimeric catharanthus alkaloids. Various separation parameters such as buffer concentration and pH, column internal diameter, and applied voltage were studied column, 72 cm (57 cm effective length) x 75 pm I.D. buffer, 0.2 M ammonium acetate solution, pH 6.2 and an applied voltage of 10 kV. Although the separation of VB and VC was the primary focus, the separation parameters determined in this study can be applied to the separation of other alkaloids as well. Separation of other alkaloids in the plant samples was observed under conditions presented in this work. A secondary objective of this study was to develop a method with experimental conditions which could be applied to electrophoresis-mass spectrometry. For this purpose, ammonium acetate buffers, which are more compatible with mass spectrometry than the widely used phosphate buffers, were used exclusively. Also, methanol-water-acetic acid was used as external buffer for the same reason [16]. 

---